Unfortunately we don't want to pivot our foot off of such a wierd angle, so we use a hierarchy to nest the buffer null underneath control nulls. We will rotate the control nulls (which will have nice world-aligned orientations) to affect the buffer nulls. The placement of the nulls are important as it gives us pivot locations for our animation.

Moving on...

Organize your schematic view by reordering the nulls and staggering their placement.

To help with visiblity for the tutorial I colored my nulls and added the itemshape plugin to each to list their names in the viewport. You dont have to color your nulls or use the itemshape plugin. Move the nulls to the locations shown.
Make sure that they line up on z with the leg chain in the other views. Also make sure that L_AnkleN is as close to L_FootB's pivot as possible. Put L_ToeC slightly below and forward of L_ToeB's pivot and with the same Y value as L_FootC. L_ToeC and L_FootC should be the physical contact points of your characters mesh with the ground for the ball and heel of the foot.

Open the options panel and disable Parent in Place. Parent L_ToeBuffer to L_ToeB. Parent L_AnkleBuffer to L_FootB.